1. Field of the Invention
The present invention relates to a lubricant for a magnetic recording device.
2. Description of the Related Art
In a magnetic recording device, reading and writing of information is carried out while a head slider having a magnetic recording transducer (in the present invention, also referred to simply as a ‘head’) flies over a hard disk which is a magnetic recording medium.
The distance between the head and a magnetic layer for recording (writing) or reproducing (reading) magnetic information on the hard disk is known as the magnetic spacing; the smaller the magnetic spacing, the greater the recording density. Meanwhile, to increase the information transfer rate, the rotational speed of the hard disk must be made high. In recent years, as the recording density and the transfer rate have been increased, there has been progress in reducing the flying height (also called floating height) and increasing in the rotational speed; currently, the head flying height has become approximately 10 nm, and the rotational speed has become approximately 15,000 rpm.
With a hard disk drive, to increase the reliability of the drive, a lubricant is applied, in a thickness of approximately 1 to 2 nm, onto the magnetic disk or the head slider, in general. This lubricant reduces friction and wear upon contact of the head with the disk, preventing the occurrence of faults.
The film thickness of the lubricant accounts for approximately 10% of the head flying height, and hence it cannot be disregarded as a factor for the magnetic spacing. Consequently, as the flying height has been reduced and the rotational speed has been increased in recent years, the properties required of the lubricant have become stricter, so that it has become almost impossible for a single component to satisfy the desired properties. There have thus been proposals to use a lubricant comprising, for example, a mixture of two lubricants (see, for example, Japanese Unexamined Patent Application Publication No. 10-143838 (claims), and No. 9-282642 (claims)). It aims at achieving both good substrate adhesion (adhesion to a substrate) and good flowability for the lubricant, by using a mixture of a low-viscosity lubricant and a high-substrate-adhesion lubricant (a lubricant with high adhesion to the substrate).
When the substrate adhesions of the two lubricants are compared, in the case of Japanese Unexamined Patent Application Publication No. 10-143838 for example, the adhesion of FOMBLIN Z TETRAOL (made by Solvay Solexis, molecular weight 2040) represented by formula (6) is markedly higher than that of FOMBLIN Z DOL (made by Solvay Solexis, molecular weight 2020) represented by formula (2). If these are mixed together and the mixture is applied onto a magnetic disk, then the flowability is increased due to the presence of the FOMBLIN Z DOL, and hence the desired film formation ability is realized. However, it has been found that, upon fast rotation, the polymer represented by formula (2) flies off and thus the amount thereof drops, whereby the proportion of the polymer represented by formula (6) increases, bringing about faulty flying.
